Image generating apparatus

ABSTRACT

In an image generating apparatus, an image combining unit combines, for each of first and second processes in sequence, first and second images to generate a composite image having a digital pixel value representing a luminance level of the corresponding pixel by a first bit width. A range setter sets, for each of the first and second processes, a target luminance-level distribution range of at least one target with respect to the composite image; the distribution range represents a range within which luminance levels of the at least one target are distributed. A dynamic range adjuster adjusts a dynamic range of the composite image generated for one of the first and second processes such that the dynamic range of the composite image generated for the corresponding one of the first and second processes matches with the target luminance-level distribution range set for the first process.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromJapanese Patent Application No. 2016-217320 filed on Nov. 7, 2016, thedisclosure of which is incorporated in its entirety herein by reference.

TECHNICAL FIELD

The present disclosure relates to image generating apparatuses forcombining plural images to thereby generate a composite image with ahigher dynamic range; the plural images are captured during respectivedifferent shutter times, i.e. exposure times, or captured at respectivedifferent shutter speeds.

BACKGROUND

High dynamic range functions (HDR functions) combine a first imagecaptured during a first shutter time with a second image captured duringa second shutter time, which is longer than the first shutter time, tothereby generate a composite image having a higher dynamic range from alow luminance level to a high luminance level.

In-vehicle cameras incorporate therein such a HDR function, and use theHDR function to increase the accuracy of detecting objects, such aswhite lines on roads and/or other vehicles. An in-vehicle cameracaptures images while its luminous environment changes when thecorresponding vehicle is travelling. This change in luminous environmentaround the in-vehicle camera changes the tone of an image captured bythe in-vehicle camera. This tone change may reduce the accuracy ofdetecting objects, such as white lines.

For addressing such a problem, Japanese Patent Application PublicationNo. 2016-96417 discloses a camera system installed in a vehicle. Thecamera system obtains information about luminous environment around thevehicle; the luminous environment changes while the vehicle istravelling. For example, the luminous environment information includesinformation about a daytime luminous environment and information about anighttime luminous environment.

The camera system captures a first image during a first shutter time,and captures a second image during a second shutter time, which islonger than the first shutter time. Then, the camera system selects oneof an automatic white-balance correcting task and a custom white-balancecorrecting task in accordance with the luminous environment to apply theselected one of the automatic white-balance correcting task and customwhite-balance correcting task to each of the first image and the secondimage. Thereafter, the camera system combines the first image with thesecond image, thus generating a composite image having a higher dynamicrange.

SUMMARY

The change in luminous environment around a camera changes, in additionto the tone of an image captured by the camera, the luminancedistribution of objects to be captured. A value of each pixel, i.e. apixel value of each pixel, of an image captured by an image sensorrepresents a luminance level of the corresponding pixel of the imagerestricted by a limited bit width, i.e. a limited number of bits. Forthis reason, even if the image captured by the camera is subjected toonly one of the white-balance correcting task and custom white-balancecorrecting task, it may be difficult to efficiently use the limitednumber of bits to express a luminance level of each pixel of thecomposite image.

This may result in, in the composite image, at least one of

1. The occurrence of blocked-up shadows or crushed shadows

2. The occurrence of blown-out highlights or clipped whites

3. The occurrence of allocation of pixel values to unused luminancelevels corresponding to no targets to be imaged

The occurrence of allocation of pixel values to unused luminance levelsmay result in coarse gray-scale of the composite image.

In view of the circumstances set forth above, one aspect of the presentdisclosure seeks to provide image generating apparatuses, which arecapable of addressing the problems set forth above.

Specifically, an alternative aspect of the present disclosure aims toprovide such image generating apparatuses, each of which is capable ofefficiently using a limited number of bits to express a luminance levelof each pixel of a composite image, the composite image being based on afirst image and a second image captured during respective first andsecond shutter times different from each other.

According to an exemplary aspect of the present disclosure, there isprovided an image generating apparatus. The image generating apparatusincludes a controller configured to cause, based on control parametersfor a camera, the camera to capture a first image based on a firstshutter time and a second image based on a second shutter time for eachof first and second processes in sequence. The first and second imageseach include at least one target to be imaged. The first shutter time islonger than the second shutter time, and the control parameters includethe first shutter time and the second shutter time. The image generatingapparatus includes an image combining unit configured to combine, foreach of the first and second processes, the first image and the secondimage to thereby generate a composite image having a digital pixel valueof each pixel thereof. The digital pixel value of each pixel representsa luminance level of the corresponding pixel by a first bit width. Theimage generating apparatus includes a range setter configured to set,for each of the first and second processes, a target luminance-leveldistribution range of the at least one target with respect to thecomposite image. The target luminance-level distribution rangerepresents a range within which luminance levels of the at least onetarget are distributed. The image generating apparatus includes acompression characteristic generator configured to generate, for each ofthe first and second processes, a compression characteristic forcompressing the digital pixel value of each pixel of the composite imageby a second bit width. The second bit width is smaller than the firstbit width. The image generating apparatus includes a compression unitconfigured to compress, in accordance with the compressioncharacteristic, the composite image for each of the first and secondprocesses to thereby generate a compressed composite image. The imagegenerating apparatus includes a dynamic range adjuster configured toadjust a dynamic range of the composite image generated for one of thefirst and second processes such that the dynamic range of the compositeimage generated for the corresponding one of the first and secondprocesses matches with the target luminance-level distribution range setby the range setter for the first process.

The dynamic range adjuster of the exemplary aspect of the presentdisclosure adjusts the dynamic range of the composite image generatedfor one of the first and second processes such that the dynamic range ofthe composite image generated for the corresponding one of the first andsecond processes matches with the target luminance-level distributionrange set by the range setter for the first process.

This enables the dynamic range of the composite image to match with thetarget luminance-level distribution range set by the range setter; theluminance levels of the at least one target are distributed within thetarget luminance-level distribution range.

This therefore prevents digital pixel values, each of which is limitedby the second bit width, i.e. the limited number of bits, from beingallocated for unused luminance levels located outside the targetluminance-level distribution range. This makes it possible toefficiently use the limited number of bits to express a correspondingluminance level of each pixel of the composite image.

The above and/or other features, and/or advantages of various aspects ofthe present disclosure will be further appreciated in view of thefollowing description in conjunction with the accompanying drawings.

Various aspects of the present disclosure can include and/or excludedifferent features, and/or advantages where applicable. In addition,various aspects of the present disclosure can combine one or morefeature of other embodiments where applicable. The descriptions offeatures, and/or advantages of particular embodiments should not beconstrued as limiting other embodiments or the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of the present disclosure will become apparent from thefollowing description of embodiments with reference to the accompanyingdrawings in which:

FIG. 1 is a block diagram schematically illustrating an example of thestructure of an image generating apparatus according to the firstembodiment of the present disclosure;

FIG. 2 is a flowchart schematically illustrating an example of an imagegeneration cycle carried out by the image generating apparatusillustrated in FIG. 1;

FIG. 3 is a graph schematically illustrating first pixel-valuecharacteristics relative to luminance levels of a first image, andsecond pixel-value characteristics relative to luminance levels of asecond image according to the first embodiment;

FIG. 4 is a graph schematically illustrating the first pixel-valuecharacteristics relative to the luminance levels of the first image, andamplified second pixel-value characteristics relative to the luminancelevels of the second image according to the first embodiment;

FIG. 5 is a graph schematically illustrating an example of an HDRcomposite image generated based on combination of the first image andthe second image, and compression characteristics generated by an imagegenerator illustrated in FIG. 1;

FIG. 6 is a graph schematically illustrating an example of a histogramof the luminance levels of the HDR composite image based on the firstimage and the second image according to the first embodiment;

FIG. 7 is a graph schematically illustrating an example of a histogramof the luminance levels of the HDR composite image in which there aretwo separated distributions according to the first embodiment;

FIG. 8 is a graph schematically illustrating a relationship between atarget luminance-level distribution range for the HDR composite imageand a current dynamic range of the HDR composite image according to thefirst embodiment;

FIG. 9 is a graph schematically illustrating a histogram of theluminance levels of the first and second images of a first scene (scene1), a target luminance-level distribution range determined based on thehistogram, and compression characteristics determined based on thetarget luminance level distribution;

FIG. 10 is a graph schematically illustrating a histogram of theluminance levels of the first and second images of a second scene (scene2), a target luminance-level distribution range determined based on thehistogram, and compression characteristics determined based on thetarget luminance level distribution;

FIG. 11 is a block diagram schematically illustrating an example of thestructure of an image generating apparatus according to the secondembodiment of the present disclosure;

FIG. 12 is a flowchart schematically illustrating an example of an imagegeneration cycle carried out by the image generating apparatusillustrated in FIG. 11;

FIG. 13 is a graph schematically illustrating a relationship between amaximum dynamic range of a camera device illustrated in FIG. 1 and thetarget luminance-level distribution range; and

FIG. 14 is a block diagram schematically illustrating an example of thestructure of an image generating apparatus according to the thirdembodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENT

The following describes embodiments of the present disclosure withreference to the accompanying drawings. In the embodiments, like partsbetween the embodiments, to which like reference characters areassigned, are omitted or simplified to avoid redundant description.

First Embodiment

The following describes an image generating apparatus 10 according tothe first embodiment of the present disclosure with reference to FIGS. 1to 10.

Referring to FIG. 1, the image generating apparatus 10, which isinstalled in a vehicle V, includes a camera device 20 and a processor30.

The camera device 20 includes an imaging unit 21 and an image generator22. The camera device 20 is, for example, mounted to a predeterminedposition of the front windshield of the vehicle V. The predeterminedposition is determined to be capable of capturing a predeterminedregion, which includes a road surface on which the vehicle V is going totravel, in front of the vehicle V. In particular, the predeterminedposition is located at the back side of the rearview mirror of thevehicle V such that the rearview mirror enables a driver of the vehicleV not to see the camera device 20.

The imaging unit 21 includes an optical system 211, an image sensor 212,an amplifier 213, and an analog-to-digital (A/D) converter 214. Theoptical system 211 is comprised of at least one lens to direct light tothe image sensor 212.

The image sensor 212 is comprised of light-sensitive elements eachincluding a charge-coupled device (CCD) or a complementarymetal-oxide-semiconductor (CMOS) switch; the light-sensitive elementsare arranged in a two-dimensional array to constitute an imaging surfaceon which the directed light is formed as an image. The two-dimensionallyarranged light-sensitive elements constitute an imaging area on whichlight output from the optical system 211 is received.

Each of the light-sensitive elements is sensitive to an amount or alevel of light; the level of light is equal to or more than apredetermined noise level and is equal to or less than a predeterminedsaturation level.

Specifically, each of the two-dimensionally arranged light-sensitiveelements, which serve as pixels, is configured to receive a component oflight directed from the optical system 211 during a shutter time ST oran exposure time. Each of the two-dimensionally arranged light-sensitiveelements is also configured to convert the intensity or luminance levelof the received light component into an analog pixel value or an analogpixel signal that is proportional to the luminance level of the receivedlight component.

The shutter time ST during which light is received by thetwo-dimensionally arranged light-sensitive elements, in other words,during which the two-dimensionally arranged light-sensitive elements areexposed to light, is a control parameter controllable by, for example,the processor 30 described later. That is, the processor 30 is capableof controlling the shutter time ST of the image sensor 212.

The shutter time ST can also be expressed as a shutter speed of theimage sensor 212. That is, the higher the shutter speed is, the shorterthe shutter time ST is.

In particular, the image sensor 212 periodically captures first andsecond images during respective first and second different shutter timesST1 and ST2; these shutter times ST1 and ST2 are control parameters setby the processor 30. Note that the first shutter time ST1 is set to belonger than the second shutter time ST2. That is, the first image can becalled a long shutter-time image, and the second image can be called ashort shutter-time image.

The amplifier 213 receives each of the first and second images. Then,the amplifier 213 amplifies the analog pixel values of each of the firstand second images by an analog gain variably controllable by theprocessor 30 described later. That is, the processor 30 is capable ofcontrolling the analog gain of the amplifier 213.

The A/D converter 214 converts the analog pixel signals (analog pixelvalues) of each of the first and second images amplified by theamplifier 213 into digital pixel signals (digital pixel values) based ona predetermined bit width, i.e. the number of bits. The bit widthaccording to the first embodiment is set to 12 bits.

The image generator 22 is designed as, for example, a hardware circuitcomprised of an image signal processor. The image generator 22 includes,for example, a combining unit 221 and a compression unit 222.

The combining unit 221 obtains the digitized first and second imagesfrom the imaging unit 21, and combines the digitized first and secondimages with each other to generate a composite image, which will bereferred to as an HDR composite image, with higher dynamic range.Dynamic range of an image represents a range of contrast of the image.The dynamic range of an image captured by the image sensor 212 during ashutter time is determined depending on the sensitivity of thelight-sensitive elements of the image sensor 212. In addition, thedynamic range of an image captured by the image sensor 212 is determineddepending on the length of the shutter time.

For example, the combining unit 221 generates a HDR composite imagehaving a digital pixel value of each pixel representing a luminancelevel of the corresponding pixel; the bit width of the digital pixelvalue of each pixel of the HDR composite image is set to 16 bits, i.e.greater than the bit width of 12 bits of each of the first and secondimages.

The compression unit 222 compresses the HDR composite image having adigital pixel value of each pixel represented by the first bit width of16 bits to thereby generate a compressed HDR composite image having adigital pixel value of each pixel represented by a second bit width of12 bits. The second bit width can be set to another bit width as long asthe second bit width is shorter than the first bit width. Thecompression unit 222 outputs, to the processor 30, the compressed HDRcomposite image having a digital pixel value of each pixel representedby the second bit width of 12 bits.

That is, the imaging unit 21 is configured to periodically generatecompressed HDR composite image, and periodically output the compressedHDR image to the processor 30.

The processor 30 is configured mainly as at least one knownmicrocomputer including a CPU 30 a, a memory device 30 b, input ports 30c 1 and 30 c 2, and an output port 30 d. The memory device 30 bincludes, for example, at least one of semiconductor memories, such as aRAM, a ROM, and a flash memory. These semiconductor memories are forexample non-transitory storage media.

Each of the input ports 30 c 1 and 30 c 2 is communicable with thecamera device 20 by wire or wireless. The output port 30 d iscommunicable with the camera device 20 by wire or wireless.

For example, the CPU 30 a of the processor 30 can run one or moreprograms, i.e. sets of program instructions, stored in the memory device30 b, thus implementing various functional modules of the processor 30as software operations. In other words, the CPU 30 a can run programsstored in the memory device 30 b, thus performing one or more routinesin accordance with the corresponding one or more programs. The aboveroutines and/or various functions of the processor 30 can be implementedas a hardware electronic circuit. For example, the various functions ofthe processor 30 can be implemented by a combination of electroniccircuits including digital circuits, which include many logic gates,analog circuits, digital/analog hybrid circuits, or hardware/softwarehybrid circuits.

Plural microcomputers can constitute the processor 30.

The functional modules implemented by the CPU 30 a include a rangesetter 31, a parameter determiner 32, an imaging controller 33, an imageprocessor 34, and an image recognizer 35.

The range setter 31 receives the HDR composite image output from theimage generator 22 at a current period via the input port 30 c 2. Then,the range setter 31 sets a target luminance-level distribution range ofluminance levels for the HDR composite image in accordance with at leastone target to be recognized from the HDR composite image; the at leastone target to be recognized will be referred to as least one recognitiontarget.

The parameter determiner 32 determines, as values of the controlparameters, a value of the first shutter time ST1, a value of the secondshutter time ST2, and a value of the analog gain in accordance with thetarget luminance-level distribution range of luminance levels for thecompressed HDR composite image.

The imaging controller 33, which serves as, for example, a dynamic rangeadjuster, controls the imaging unit 21 in accordance with the determinedvalues of the control parameters, i.e. the first shutter time ST1, thesecond shutter time ST2, and the analog gain, thus capturing a nextfirst image and a next second image at a next period.

The image processor 34 discards the predetermined lowest-order bits fromthe 12-bit digital pixel value of each pixel of the compressed HDRcomposite image output from the imaging unit 21. For example, the imageprocessor 34 discards the lowest-order four bits from the 12-bit digitalpixel value of each pixel of the compressed HDR composite image, thusoutputting an output image having a 8-bit digital pixel value of eachpixel to the image recognizer 35.

The image recognizer 35 is configured to be capable of handling datahaving 8 bits or less, and to recognize, from the output image, at leastone recognition target. Then, the image recognizer 35 is configured tooutput the recognition result to the ECU 100.

Next, the following describes an image generation cycle, i.e. an imagegeneration process, carried out by the image generating apparatus 10with reference to FIG. 2. That is, the image generating apparatus 10periodically performs the image generation cycle in predeterminedintervals.

In step S10 of a current image generation cycle, the imaging controller33 controls the imaging unit 21 using the control parameters to causethe imaging unit 21 to capture first and second images during respectivefirst and second different shutter times ST1 and ST2. The controlparameters used in the current image generation cycle have beendetermined by the parameter determiner 32 in step S40 of the previousimage generation cycle. The second shutter time ST2 according to thefirst embodiment is set to 1.25 [ms], and the first shutter time ST1according to the first embodiment is set to 20 [ms].

In step S10, the imaging unit 21 amplifies each of the first and secondimages by the analog gain, and converts the analog pixel signals (analogpixel values) of each of the amplified first and second images intodigital pixel signals (digital pixel values) based on the predeterminedbit width of 12 bits.

Next, the image generator 22 obtains the digitized first and secondimages sent from the imaging unit 21, and combines the digitized firstand second images with each other to generate an HDR composite image instep S20.

FIG. 3 illustrates a graph representing first pixel-valuecharacteristics PV1 relative to luminance levels of the first image, andsecond pixel-value characteristics PV2 relative to luminance levels ofthe second image. The graph has a vertical axis indicative of thedigital pixel values of each of the first and second images, and ahorizontal axis indicative of the corresponding luminance levels of thecorresponding one of the first and second images. Because the shuttertime ST1 is set to be 16 times as long as the shutter time ST2, theamount of light received by the imaging area of the image sensor 212 forthe first image is 16 times larger than the amount of light received bythe imaging area of the image sensor 212 for the second image. For thisreason, each of the digital pixel values of the first image of a targetis 16 times larger than the corresponding digital pixel value of thesecond image of the same target although the luminance level of thetarget are unchanged.

For this reason, in step S20, the image generator 22 obtains the ratioof the first shutter time ST1 to the second shutter time ST2, andamplifies the digital pixel values of the second image by the obtainedratio as a digital gain to thereby match the second pixel-valuecharacteristics PV2 with the first pixel-value characteristics PV1. Theamplified second pixel-value characteristics PV2 are illustrated byreference character PV2A in FIG. 4. That is, this enables the digitalpixel value of each pixel of the second image and the digital pixelvalue of the corresponding pixel of the first image to represent thesame luminance level.

Specifically, the ratio of the first shutter time ST1 to the secondshutter time ST2 is 16, so that the image generator 22 multiplies thedigital pixel values of the second image by 16. This results in theluminance level of each pixel of the second image being represented asthe first bit width, i.e., 16-bit width. That is, the digital pixelvalue of each pixel of the second image is within the range from 00000to 65535.

For example, the image generator 22 is configured to

1. Select one of the digital pixel value of the corresponding pixel ofthe first image and the digital pixel value of the corresponding pixelof the second image or

2. Merge two of the digital pixel value of each pixel of the first imageand the digital pixel value of the corresponding pixel of the secondimage

In particular, the image generator 22 is configured to, for example,select the digital pixel values of the first image, i.e. the longshutter-time image, for a lower luminance-level region of the compositeimage, and select the digital pixel values of the second image, i.e. theshort shutter-time image, for a higher luminance-level region of thecomposite image.

FIG. 5 illustrates an example of the HDR composite image generated basedon combination of the first image and the second image using thereference character CI; the digital pixel value of each pixel of the HDRcomposite image CI is expressed by the first bit width, i.e., 16-bitwidth.

Next, in step S30, the range setter 31 sets a target luminance-leveldistribution range of at least one recognition target with respect tothe HDR composite image generated in step S20.

FIG. 6 illustrates an example of a histogram H of the luminance levelsof the HDR composite image based on the first image (long shutter-timeimage) and the second image (short shutter-time image) as a graph whosehorizontal axis represents the luminance levels of the HDR compositeimage, and whose vertical axis represents the number of pixelscorresponding to each luminance level of the HDR composite image. Inother words, the vertical axis of the graph represents the frequency ofoccurrence of pixels corresponding to each luminance level of the firstand second images.

As illustrated in FIG. 6, the luminance levels of the first image (longshutter-time image) are distributed in a relatively lower region in thehistogram H, and the luminance levels of the second image (shortshutter-time image) are distributed in a relatively higher region in thehistogram H. In step S30, the target luminance-level distribution rangeis defined as a luminance-level distribution range of the histogram Hfrom a variable lower limit level LL to a variable upper limit level UL.

Specifically, in step S30, the range setter 31 sets a value of the upperlimit level UL such that the number of pixels of luminance levels of theHDR composite image, which are higher than the upper limit level UL, issmaller than a predetermined high-contrast threshold. Additionally, instep S30, the range setter 31 sets a value of the lower limit level LLsuch that the number of pixels of luminance levels of the HDR compositeimage, which are lower than the lower limit level LL, is smaller than apredetermined low-contrast threshold.

The high-contrast threshold is previously determined to be a value thatprevents the occurrence of blown-out highlights or clipped whites of anestimated higher luminance-level object, and the low-contrast thresholdis previously determined to be a value that prevents the occurrence ofblocked-up shadows or crushed shadows of an estimated lowerluminance-level object.

In step S30, if there are two separated histograms of some luminancelevels of the HDR composite image and one of the two separatedhistograms is located to be higher than a predetermined upper limitthreshold, the range setter 31 eliminates the separated histogram, whichis located to be higher than the predetermined upper limit threshold,from the luminance levels of the HDR composite image, thus setting thetarget luminance-level distribution range about the remaining separatedhistogram, i.e. the remaining distribution of the luminance levels. Theupper limit threshold is previously determined to be a luminance level;the luminance level is located outside a predetermined luminance levelrange that recognition targets, such as pedestrians and other vehicles,to be captured by the camera device 20 can have normally. In otherwords, objects having very high luminance levels higher than the upperlimit threshold may be light sources, such as the sun or fluorescentlamps, so that they can be eliminated from recognition targets to becaptured by the camera device 20.

For example, if there are two separated distributions H1 and H2 of theluminance levels of the HDR composite image and the separateddistribution H2 is located to be higher than the predetermined upperlimit threshold, the range setter 31 eliminates the separateddistribution H2, thus setting the target luminance-level distributionrange about the remaining separated distribution H1 (see FIG. 7).

That is, the target luminance-level distribution range for the HDRcomposite image represents a target dynamic range for the HDR compositeimage.

Next, the parameter determiner 32 determines a value of at least one ofthe control parameters including the first shutter time ST1, the secondshutter time ST2, and the analog gain in accordance with the targetluminance-level distribution range in step S40.

FIG. 8 schematically illustrates a relationship between the targetluminance-level distribution range, i.e. a target dynamic range, for theHDR composite image and a current dynamic range of the HDR compositeimage. Specifically, FIG. 8 shows that the current dynamic range of theHDR composite image is insufficient to satisfy the target dynamic range.

In detail, as illustrated in a circled portion A in FIG. 8, the currentdynamic range of the HDR composite image at its lowest luminance-levelportion is insufficient to satisfy the target dynamic range at itslowest luminance-level portion. This may result in a correspondingportion of the at least one recognition target included in the HDRcomposite image becoming blocked-up shadows or crushed shadows.Additionally, as illustrated in a circled portion B in FIG. 8, thecurrent dynamic range of the HDR composite image at its highestluminance-level portion is insufficient to satisfy the target dynamicrange at its highest luminance-level portion. This may result in acorresponding portion of the at least one recognition target included inthe HDR composite image being saturated, so that the correspondingportion of the at least one recognition target included in the HDRcomposite image may have blown-out highlights or clipped whites.

On the other hand, if the current dynamic range of the HDR compositeimage is wider than the target luminance-level distribution range,unused luminance levels corresponding to no recognition targets may beincluded in the HDR composite image.

For addressing such a situation, the parameter determiner 32 calculatesa value of at least one of the control parameters including the firstshutter time ST1, the second shutter time ST2, and the analog gain instep S40; the value of at least one of the control parameters isrequired to match the current dynamic range of the HDR composite imagewith the target dynamic range, i.e. the target luminance-leveldistribution range, set in step S30.

Specifically, the parameter determiner 32 determines a value of thefirst shutter time ST1 to be longer if the current dynamic range of theHDR composite image at its lowest luminance-level portion isinsufficient to satisfy the target dynamic range at its lowestluminance-level portion. This enables a luminance level lower than thelowest luminance level of the current dynamic range to be set to 00001,thus extending the current dynamic range in the darker direction(luminance-level lower direction).

In addition, the parameter determiner 32 determines a value of thesecond shutter time ST2 to be shorter if the current dynamic range ofthe HDR composite image at its highest luminance-level portion isinsufficient to satisfy the target dynamic range at its highestluminance-level portion. This enables a luminance level higher than thehighest luminance level of the current dynamic range to be set to themaximum value based on the first bit width, i.e. 16-bit width; themaximum value is 65535.

If the lowest luminance level of the current dynamic range of the HDRcomposite image does not cover the lowest luminance level of the targetdynamic range in spite of the fact that the first shutter time ST1 hasreached its upper limit, the parameter determiner 32 determines, i.e.adjusts, a value of the analog gain to thereby extend the currentdynamic range in the darker direction (luminance-level lower direction).

Note that the determined value of at least one of the control parametersis used for the image controller 33 in step S10 of the next currentimage generation cycle set forth above. That is, if no new values of theremaining control parameter(s) are determined in step S10, the values ofthe remaining control parameter(s), which have been used for the imagecontroller 33 in step S10 of the current image generation cycle, arealso used for the image controller 33 in step S10 of the next currentimage generation cycle.

Next, in step S50, the image generator 22 generates compressioncharacteristics CC for compressing the HDR composite image generated instep S20.

Because the HDR composite image, which is generated based on combinationof the first and second images having the respective different shuttertimes ST1 and ST2, has a digital pixel value of each pixel representedby the first bit width, i.e., 16-bit width. That is, the first bit widthof the digital pixel value of each pixel of the HDR composite image islonger than the 8-bit width recognizable by the image recognizer 35.

For this reason, the image generator 22 is configured to compress theHDR composite image whose bit width of each pixel is changed from 16bits to 8 bits.

First, the image generator 22 generates the compression characteristicsCC that express the luminance levels of the HDR composite image withinthe current dynamic range or the target dynamic range by digital pixelvalues of 12-bit width.

An example of the compression characteristics generated by the imagegenerator 22 is illustrated in FIG. 5 as a graph format.

Specifically, the compression characteristics CC illustrated in FIG. 5have

1. A predetermined first compression rate C1 for the luminance level ofa pixel of the HDR composite image being within a predetermined lowluminance-level region LR1 that is defined to be lower than apredetermined first luminance level L1

2. A predetermined second compression rate C2 for the luminance level ofa pixel of the HDR composite image being within a predetermined middleluminance-level region LR2 that is defined to be equal to or higher thanthe first luminance level L1 and lower than a predetermined secondluminance level L2; the second compression rate C2 is higher than thefirst compression rate C1

3. A predetermined third compression rate C3 for the luminance level ofa pixel of the HDR composite image being within a predetermined highluminance-level region LR3 that is defined to be equal to or higher thanthe second luminance level L2 and lower than a predetermined thirdluminance level L3 corresponding to the highest luminance level of thedynamic range; the third compression rate C3 is higher than the secondcompression rate C2

In other words, a compression rate of the compression characteristics ischanged from the first compression rate C1 to the second compressionrate C2 at the first luminance level L1, and also changed from thesecond compression rate C2 to the third compression rate C3 at thesecond luminance level L2.

The image generator 22 sets the first compression rate C1 of thecompression characteristics CC to 1, i.e. sets no compression of thecompression characteristics CC within the low luminance-level region LR1if the at least one recognition target in the HDR composite image is apedestrian during night-time, because the body trunk of the pedestrianduring night-time, on which no headlight is likely to fall, has lowluminance levels. In addition, the image generator 22 sets the secondcompression rate C2 of the compression characteristics CC within themiddle luminance-level region LR2 to be higher than the firstcompression rate of 1.

In addition, the image generator 22 sets the third compression rate C3within the high luminance-level region LR3 to be higher than the secondcompression rate C2, because the leg portion of the pedestrian duringnight-time, on which headlight is likely to fall, has high luminancelevels.

In other words, the image generator 22 generates the compressioncharacteristics CC such that

(1) No compression is carried out for the digital pixel values of theHDR composite image within the low luminance-level region LR1 to therebyenable the HDR composite image to have the digital pixel values of thefirst image themselves within the low luminance-level region LR1

(2) High compression is carried out for the digital pixel values of theHDR composite image within each of the middle luminance-level region LR2and the high luminance-level region LR3

(3) The wider the target luminance-level distribution range is, thehigher the compression rate for the digital pixel values of the HDRcomposite image within the high luminance-level region LR3 isSubsequently, the image generator 22 compresses, based on thecompression characteristics CC generated in step S50, the HDR compositeimage having a digital pixel value of each pixel represented by thefirst bit width of 16 bits to thereby generate a compressed HDRcomposite image having a digital pixel value of each pixel representedby the second bit width of 12 bits in step S60. Then, the imagegenerator 22 sends the compressed HDR composite image to the imageprocessor 34 in step S60.

The image processor 34 discards the lowest-order four bits from the12-bit digital pixel value of each pixel of the compressed HDR compositeimage sent from the image generator 22, thus outputting an output imagehaving a 8-bit digital pixel value of each pixel to the image recognizer35. Thereafter, the image generating apparatus 10 terminates the currentimage generation cycle, and thereafter returns to step S10, thusperforming the next image generation cycle.

Next, the following describes a first example indicative of how theimage generating apparatus 10 operates to generate an HDR compositeimage, and a second example indicative of how the image generatingapparatus 10 operates to generate an HDR composite image.

FIG. 9 schematically illustrates

1. A histogram H10 of the luminance levels of the first and secondimages, each of which is generated by capturing a first scene by thecamera device 20 in an (m−1)-th image generation cycle where m is aninteger more than 2

2. A target luminance-level distribution range set as a luminance-leveldistribution range of the histogram H10 in the (m−1)-th image generationcycle

3. Compression characteristics CC1 generated by the image generator 22in the (m−1)-th image generation cycle according to the first example

FIG. 10 also schematically illustrates

1. A histogram H11 of the luminance levels of the first and secondimages, each of which is generated by capturing a second scene by thecamera device 20 in an (n−1)-th image generation cycle where n is aninteger more than 2

2. A target luminance-level distribution range set as a luminance-leveldistribution range of the histogram H11 in the (n−1)-th image generationcycle

3. Compression characteristic CC2 generated by the image generator 22 inthe (n−1)-th image generation cycle according to the second example.

For example, the first scene is a scene captured by the camera device 20as the first and second images during daytime, and the second scene,which is different from the first scene, is a scene captured by thecamera device 20 when the vehicle V is travelling at the exit of atunnel.

FIG. 9 shows that the target luminance-level distribution range is setin accordance with the histogram H10, and a value of at least one of thecontrol parameters is determined such that the dynamic range of the HDRcomposite image in the (m−1)-th image generation cycle matches with thetarget luminance-level distribution range.

Thereafter, first and second images are captured in the next m-th imagegeneration cycle in accordance with the determined value of the at leastone of the control parameters, so that an HDR composite image isgenerated based on the first and second images in the m-th imagegeneration cycle. The dynamic range of the HDR composite image generatedin the m-th image generation cycle is substantially matched with thetarget luminance-level distribution range set in the (m−1)-th imagegeneration cycle.

Allocating digital pixel values of 12-bit width to the respectiveluminance levels of the HDR composite image within the dynamic range ofthe HDR composite image, i.e. within the target luminance-leveldistribution range of at least one recognition target in the HDRcomposite image, so that a compressed HDR composite image is generated.

The compression characteristics CC1 of the HDR composite image for thescene 1 have

1. A predetermined first compression rate C11 for the luminance level ofa pixel of the HDR composite image being within a predetermined lowluminance-level region LR11 that is defined to be lower than apredetermined first luminance level L11

2. A predetermined second compression rate C12 for the luminance levelof a pixel of the HDR composite image being within a predeterminedmiddle luminance-level region LR12 that is defined to be equal to orhigher than the first luminance level L11 and lower than a predeterminedsecond luminance level L12; the second compression rate C12 is higherthan the first compression rate C11

3. A predetermined third compression rate C13 for the luminance level ofa pixel of the HDR composite image being within a predetermined highluminance-level region LR13 that is defined to be equal to or higherthan the second luminance level L12 and lower than a predetermined thirdluminance level L13 corresponding to the highest luminance level of thedynamic range; the third compression rate C13 is higher than the secondcompression rate C12

Similarly, the compression characteristics CC2 of the HDR compositeimage for the scene 2 have

1. A predetermined first compression rate C21 for the luminance level ofa pixel of the HDR composite image being within a predetermined lowluminance-level region LR21 that is defined to be lower than apredetermined first luminance level L21

2. A predetermined second compression rate C22 for the luminance levelof a pixel of the HDR composite image being within a predeterminedmiddle luminance-level region LR22 that is defined to be equal to orhigher than the first luminance level L21 and lower than a predeterminedsecond luminance level L22; the second compression rate C22 is higherthan the first compression rate C21

3. A predetermined third compression rate C23 for the luminance level ofa pixel of the HDR composite image being within a predetermined highluminance-level region LR23 that is defined to be equal to or higherthan the second luminance level L22 and lower than a predetermined thirdluminance level L23 corresponding to the highest luminance level of thedynamic range; the third compression rate C23 is higher than the secondcompression rate C22

That is, the dynamic range of the HDR composite image for the firstscene is wider than the dynamic range of the HDR composite image for thesecond scene.

For this reason, the first compression rate C11 for the luminance levelof a pixel of the HDR composite image being within the lowluminance-level region LR11 is identical to the second compression rateC21 for the luminance level of a pixel of the HDR composite image beingwithin the low luminance-level region LR21. In contrast, the thirdcompression rate C13 for the luminance level of a pixel of the HDRcomposite image being within the high luminance-level region LR21 ishigher than the third compression rate C23 for the luminance level of apixel of the HDR composite image being within the high luminance-levelregion LR23.

As described above, the image generation apparatus 10 is configured toset all the luminance levels of the HDR composite image within thetarget luminance-level distribution range to respective digital pixelvalues. This configuration therefore reduces allocation of digital pixelvalues to luminance levels of the HDR composite image; the luminancelevels correspond to no recognition targets in the HDR composite image.This configuration also ensure that digital pixel values are allocatedto the luminance levels of at least one recognition target in the HDRcomposite image.

The above first embodiment of the present disclosure achieves thefollowing first to fifth advantageous effects.

The image generating apparatus 10 according to the first embodiment isconfigured to determine a value of at least one of the controlparameters that control the imaging unit 21 to thereby generate an HDRcomposite image whose dynamic range matches with the targetluminance-level distribution range within which the luminance levels ofat least one recognition target included in the HDR composite image aredistributed. The image generating apparatus 10 is also configured toallocate limited digital pixel values restricted by a predetermined bitwidth to the dynamic range of the generated HDR composite image.

This configuration achieves the first advantageous effect of reducingallocation of digital pixel values to luminance levels of the HDRcomposite image; the luminance levels correspond to no recognitiontargets in the HDR composite image. This therefore enables digital pixelvalues to be allocated to the luminance levels of at least onerecognition target in the HDR composite image.

The image generating apparatus 10 according to the first embodiment isconfigured to capture first and second images based on the determinedcontrol parameters to thereby match the dynamic range of an HDRcomposite image generated based on the first and second images with thetarget luminance-level distribution range. This configuration achievesthe second advantageous effect of generating a clearer output imagebased on the HDR composite image to the image recognizer 35 as comparedwith an output image, which is obtained by manipulating an HDR compositeimage to thereby match the dynamic range of the HDR composite image withthe target luminance-level distribution range. This configuration alsoreduces processing load of the image generating apparatus 10.

The image generating apparatus 10 is configured to set the targetluminance-level distribution range such that the number of pixels ofluminance levels, which are higher than the upper limit level UL, issmaller than the predetermined high-contrast threshold. Thisconfiguration therefore achieves the third advantageous effect ofpreventing the occurrence of blocked-up shadows or crushed shadow of atleast one recognition target.

The image generating apparatus 10 is configured to set the targetluminance-level distribution range such that the number of pixels ofluminance levels, which are lower than the lower limit level LL, issmaller than the predetermined low-contrast threshold. Thisconfiguration achieves the fourth advantageous effect of preventing theoccurrence of blown-out highlights or clipped whites of at least onerecognition target.

The image generating apparatus 10 is configured to set the targetluminance-level distribution range while eliminating luminance-leveldistributions that are higher than the upper limit threshold. Thisconfiguration achieves the fifth advantageous effect of eliminatingobjects, which are clearly different from at least one recognitiontarget, from the target luminance-level distribution range, thusallocating digital pixel values to the luminance levels of at least onerecognition target in the HDR composite image.

Second Embodiment

The following describes the second embodiment of the present disclosurewith reference to FIGS. 11 to 13.

An image generating apparatus 10A according to the second embodimentdiffers from the image generating apparatus 10 in the following points.So, the following mainly describes the different points of the imagegenerating apparatus 10A according to the second embodiment, and omitsor simplifies descriptions of like parts between the first and secondembodiments, to which identical or like reference characters areassigned, thus eliminating redundant description.

The image generating apparatus 10 according to the first embodiment isconfigured to determine a value of at least one of the controlparameters that control the imaging unit 21 to thereby generate an HDRcomposite image whose dynamic range matches with the targetluminance-level distribution range within which the luminance levels ofat least one recognition target included in the HDR composite image aredistributed.

In contrast, the image generating apparatus 10A according to the secondembodiment is configured to generate an HDR composite image whosedynamic range has a maximum width. The dynamic range having its maximumwidth will be referred to as a maximum dynamic range. Then, the imagegenerating apparatus is configured to manipulate the HDR composite imageto thereby clip, i.e. extract, a corrected HDR composite image whosedynamic range is adjusted to match with the target luminance-leveldistribution range. The maximum dynamic range of the HDR composite imageis previously determined depending on the design specifications of thecamera device 20, which include the sensitivity of the light-sensitiveelements of the image sensor 212, and the maximum and minimum values ofthe shutter time ST of the camera device 20.

Specifically, as illustrated in FIG. 11, in the image generatingapparatus 10A, an image generator 22A does not include the compressionunit 222, so that the image generator 22A generates and outputs an HDRcomposite image having a digital pixel value of each pixel representedby the first bit width of 16 bits to an image processor 34A of theprocessor 30.

The image processor 34A of the image generating apparatus 10A serves asboth the range setter 31 and the compression unit 222 according to thefirst embodiment, so that the range setter 31 is eliminated from theprocessor 30.

Additionally, the image generating apparatus 10A is configured toperiodically carry out an image generation cycle, i.e. an imagegeneration process, which is partially different from the imagegeneration cycle illustrated in FIG. 2, with reference to FIG. 12.

In step S100 of a current image generation cycle, the parameterdeterminer 32 determines a value of at least one of the controlparameters including the first shutter time ST1, the second shutter timeST2, and the analog gain such that the dynamic range of an HDR compositeimage generated based on the control parameters matches with the maximumdynamic range.

Next, in step S110, the imaging controller 33 controls the imaging unit21 using the control parameters determined in step S100 to cause theimaging unit 21 to capture first and second images during respectivefirst and second different shutter times ST1 and ST2, which is similarto the operation in step S10. In step S110, the imaging unit 21 alsoamplifies each of the first and second images by the analog gain, andconverts the analog pixel signals (analog pixel values) of each of theamplified first and second images into digital pixel signals (digitalpixel values) based on the predetermined bit width of 12 bits, which issimilar to the operation in step S10.

Next, in step S120, the image generator 22A obtains the digitized firstand second images sent from the imaging unit 21, and combines thedigitized first and second images with each other to generate an HDRcomposite image, which is similar to the operation in step S20. Thedigital pixel value of each pixel of the HDR composite image generatedin step S120 is expressed by the first bit width, i.e. 16-bit width, andthe dynamic range of the HDR composite image generated in step S120 isset to the maximum dynamic range. The HDR composite image is sent fromthe image generator 22 to the image processor 34A.

Next, in step S130, the image processor 34A, which serves as, forexample, the range setter to set a target luminance-level distributionrange of at least one recognition target with respect to the HDRcomposite image generated in step S120, which is similar to theoperation in step S30.

Like FIG. 6, FIG. 13 schematically illustrates a histogram HA of theluminance levels of the first image (long shutter-time image) and thesecond image (short shutter-time image). FIG. 13 also schematicallyillustrates the maximum dynamic range of the HDR composite image.

Following the operation in step S130, the image processor 34A serves as,for example, a dynamic range adjuster to clip, i.e. obtain, from the HDRcomposite image generated in step S120, a corrected HDR image whosedynamic range matches with the target luminance-level distribution range(see FIG. 13). Then, the image processor 34 updates the HDR compositeimage generated in step S120 to the corrected HDR composite image.

Next, in step S150, the image processor 34A serves as, for example, acompression unit to generate compression characteristics CC forcompressing the corrected HDR composite image generated in step S140,which is similar to the operation in step S50.

Subsequently, in step S160, the image processor 34A serves as, forexample, the compression unit to compress, based on the compressioncharacteristics CC generated in step S150, the corrected HDR compositeimage having a digital pixel value of each pixel represented by thefirst bit width of 16 bits to thereby generate a compressed HDRcomposite image having a digital pixel value of each pixel representedby the second bit width of 12 bits in step S160.

In step S160, the image processor 34A discards lowest-order four bitsfrom the 12-bit digital pixel value of each pixel of the compressed HDRcomposite image, thus outputting an output image having a 8-bit digitalpixel value of each pixel to the image recognizer 35. Thereafter, theimage generating apparatus 10A terminates the current image generationcycle, and thereafter returns to step S100, thus performing the nextimage generation cycle.

The above second embodiment of the present disclosure achieves thefollowing sixth advantageous effect in addition to the third to fifthadvantageous effects set forth above.

Specifically, the image generating apparatus 10A is configured togenerate an HDR composite image whose dynamic range is set to themaximum dynamic range, and clip, from the HDR composite image, acorrected HDR composite image whose dynamic range matches with thetarget luminance-level distribution range. This configuration thereforereduces allocation of digital pixel values to luminance levels of theHDR composite image; the luminance levels correspond to no recognitiontargets in the HDR composite image. This therefore enables digital pixelvalues to be allocated to the luminance levels of at least onerecognition target in the HDR composite image.

Third Embodiment

The following describes the third embodiment of the present disclosure.

An image generating apparatus 10B according to the third embodimentdiffers from the image generating apparatus 10A in the following points.So, the following mainly describes the different points of the imagegenerating apparatus 10B according to the third embodiment, and omits orsimplifies descriptions of like parts between the second and thirdembodiments, to which identical or like reference characters areassigned, thus eliminating redundant description.

The image generating apparatus 10A according to the second embodiment isconfigured such that the image processor 34A generates a corrected HDRcomposite image whose dynamic range is adjusted to match with the targetluminance-level distribution range.

In contrast, referring to FIG. 14, the image generating apparatus 10Bincludes an image generator 22B in place of the image generator 22A.

Specifically, the image generator 22B, i.e. the combining unit 221,obtains the digitized first and second images sent from the imaging unit21, and combines the digitized first and second images with each otherto generate an HDR composite image (see step S120).

Next, the image generator 22B includes an image processing circuit 221A,which serves as, for example, the range setter to set a targetluminance-level distribution range of at least one recognition targetwith respect to the HDR composite image generated in step S120 (see stepS130).

The image processing circuit 221A of the generator 22B also serves as,for example, a dynamic range adjuster to clip, from the HDR compositeimage generated in step S120, a corrected HDR image whose dynamic rangematches with the target luminance-level distribution range, thusupdating the HDR composite image generated in step S120 to the correctedHDR composite image (see step S140).

Next, the image generator 22B, i.e. the compression unit 222, generatescompression characteristics CC for compressing the corrected HDRcomposite image generated in step S140 (see step S150), and compresses,based on the compression characteristics CC generated in step S150, thecorrected HDR composite image having a digital pixel value of each pixelrepresented by the first bit width of 16 bits to thereby generate acompressed HDR composite image having a digital pixel value of eachpixel represented by the second bit width of 12 bits (see step S160).

Then, the image processor 34 discards predetermined lowest-order bitsfrom the 12-bit digital pixel value of each pixel of the compressed HDRcomposite image output from the imaging unit 21. For example, the imageprocessor 34 discards the lowest-order four bits from the 12-bit digitalpixel value of each pixel of the compressed HDR composite image, thusoutputting an output image having a 8-bit digital pixel value of eachpixel to the image recognizer 35.

That is, the image generator 22B is programmed to perform the operationsin steps S120 to S140, and the image processor 34 is programmed toperform the operations in steps S150 and S160.

The above third embodiment of the present disclosure achieves the abovesixth advantageous effect in addition to the third to fifth advantageouseffects set forth above.

The present disclosure is not limited to the descriptions of the firstto third embodiments, and the descriptions of each of the first to thirdembodiments can be widely modified within the scope of the presentdisclosure.

In each of the first to third embodiments, the shutter time ST is set tothe first shutter time ST1 and the second shutter time ST2, but thepresent disclosure is not limited thereto. Specifically, the shuttertime ST can be set to first to third shutter times ST1 to ST3, which arearranged in descending order, and an HDR composite image can begenerated based on the first to third shutter times ST1 to ST3.Additionally, the shutter time ST can be set to four or more shuttertimes, and an HDR composite image can be generated based on the four ormore shutter times

The functions of one element in each of the first to third embodimentscan be distributed as plural elements, and the functions that pluralelements have can be combined into one element. At least part of thestructure of each of the first to third embodiments can be replaced witha known structure having the same function as the at least part of thestructure of the corresponding embodiment. A part of the structure ofeach of the first to third embodiments can be eliminated. At least partof the structure of each of the first to third embodiments can be addedto or replaced with the structures of the other embodiment. All aspectsincluded in the technological ideas specified by the language employedby the claims constitute embodiments of the present invention.

The present disclosure can be implemented by various embodiments inaddition to the image generating apparatus; the various embodimentsinclude systems each including the image generating apparatus, programsfor serving a computer as one of the image generating apparatuses,storage media storing the programs, and image generating methods.

While the illustrative embodiment of the present disclosure has beendescribed herein, the present disclosure is not limited to theembodiment described herein, but includes any and all embodiments havingmodifications, omissions, combinations (e.g., of aspects across variousembodiments), adaptations and/or alternations as would be appreciated bythose having ordinary skill in the art based on the present disclosure.The limitations in the claims are to be interpreted broadly based on thelanguage employed in the claims and not limited to examples described inthe present specification or during the prosecution of the application,which examples are to be construed as non-exclusive.

What is claimed is:
 1. An image generating apparatus comprising: acontroller configured to cause, based on control parameters for acamera, the camera to capture a first image based on a first shuttertime and a second image based on a second shutter time for each of firstand second processes in sequence, the first and second images eachincluding at least one target to be imaged, the first shutter time beinglonger than the second shutter time, the control parameters includingthe first shutter time and the second shutter time; an image combiningunit configured to combine, for each of the first and second processes,the first image and the second image to thereby generate a compositeimage having a digital pixel value of each pixel thereof, the digitalpixel value of each pixel representing a luminance level of thecorresponding pixel by a first bit width; a range setter configured toset, for each of the first and second processes, a targetluminance-level distribution range of the at least one target withrespect to the composite image, the target luminance-level distributionrange representing a range within which luminance levels of the at leastone target are distributed; a compression characteristic generatorconfigured to generate, for each of the first and second processes, acompression characteristic for compressing the digital pixel value ofeach pixel of the composite image by a second bit width, the second bitwidth being smaller than the first bit width; a compression unitconfigured to compress, in accordance with the compressioncharacteristic, the composite image for each of the first and secondprocesses to thereby generate a compressed composite image; and adynamic range adjuster configured to adjust a dynamic range of thecomposite image generated for one of the first and second processes suchthat the dynamic range of the composite image generated for thecorresponding one of the first and second processes matches with thetarget luminance-level distribution range set by the range setter forthe first process.
 2. The image generating apparatus according to claim1, wherein: the dynamic range adjuster is configured to determine, forthe second process, a value of at least one of the control parameterssuch that the dynamic range of the composite image generated for thesecond process matches with the target luminance-level distributionrange set by the range setter for the first process.
 3. The imagegenerating apparatus according to claim 1, wherein: the controlparameters for the current image generating process for the firstprocess are determined such that the dynamic range of the compositeimage for the first process matches with a maximum dynamic rangepreviously determined by design specifications of the camera; and thedynamic range adjuster is configured to extract, from the compositeimage generated by the image combining unit for the first process, acorrected composite image whose dynamic range matches with the targetluminance-level distribution range set by the range setter for the firstprocess, the compression unit being configured to compress, inaccordance with the compression characteristic, the corrected compositeimage for the first process as the composite image.
 4. The imagegenerating apparatus according to claim 1, wherein: the controlparameters for the current image generating process for the firstprocess are determined such that the dynamic range of the compositeimage for the first process matches with a maximum dynamic rangepreviously determined by design specifications of the camera; and thedynamic range adjuster is installed in the camera and is configured toclip, from the composite image generated by the image combining unit forthe first process, a corrected composite image whose dynamic rangematches with the target luminance-level distribution range set by therange setter for the first process.
 5. The image generating apparatusaccording to claim 1, wherein: the range determiner is configured to setthe target luminance-level distribution range such that the number offirst pixels of luminance levels of the composite image is smaller thana predetermined high-contrast threshold, the luminance levels of thefirst pixels being higher than a predetermined upper limit.
 6. The imagegenerating apparatus according to claim 1, wherein: the range determineris configured to set the target luminance-level distribution range suchthat the number of second pixels of luminance levels of the compositeimage is smaller than a predetermined low-contrast threshold, theluminance levels of the second pixels being lower than a predeterminedlower limit.
 7. The image generating apparatus according to claim 1,wherein: the range determiner is configured to eliminate at least oneluminance level from the luminance levels of the composite image tothereby set the target luminance-level distribution range based on theremaining luminance levels of the composite image if the at least oneluminance level is higher than a predetermined upper limit threshold.